Employing ELT software technologies for the upgrade of the FORS instrument at ESO VLT

FORS (FOcal Reducer/low dispersion Spectrograph) is a multi-mode (imaging, polarimetry, long slit and multi-object spectroscopy) optical instrument mounted at the Cassegrain focus of one of the Unit Telescopes of ESO's Very Large Telescope (VLT). Since FORS is a workhorse and quite unique instrument in Paranal, there is a strong need to upgrade it, both to address possible new scientific goals and to ensure regular instrument availability for the forthcoming years. The current instrument control software and electronics have been developed at the end of the '90s, and several parts are becoming obsolete and do not follow the latest standards imposed by ESO for the VLT instruments. An initial collaboration has been setup between ESO and INAF - Astronomical Observatory of Trieste in 2018 for the feasibility study of the upgrade of the FORS control software and electronics with the latest VLT standard technologies (FORS-Up project). In the last years, however, ESO is developing new software and electronics control standards for the forthcoming ELT telescope with the aim to develop a full-fledged control system able to efficiently fight hardware obsolescence, offer modern software tools, lower costs, integration and maintenance efforts, and easy installation. This paper focuses on the FORS-Up control system based on the ELT Instrument Control Software Framework as presented at the FORS-Up Final Design Review in October 2021.